The present invention relates to a magnetic recording medium and its production method and a magnetic recording apparatus. Particularly, it relates to a magnetic recording medium carrying out recording and reproducing by a flying/contact magnetic head and its production method and a magnetic recording medium.
A magnetic recording apparatus represented by a magnetic disk apparatus (hard disk drive) has been widely used as an outboard recording apparatus of an information processing apparatus such as a computer, and in recent years, it has been used also as a recording apparatus for dynamic images or as a recording apparatus for a set-top box.
A magnetic disk apparatus usually consists of a shaft which fixes one or plurality of magnetic disks in a skewered state, a motor which is bonded to said shaft by means of a bearing and which rotates the magnetic disk, a magnetic head which is used for recording and/or reproducing, an arm to which said head is attached, and an actuator capable of moving the head to an optional position on the magnetic recording medium by means of the head arm. The head for recording and reproducing is usually a flying head, and moves on the magnetic recording medium with a certain flying height.
Further, in addition to the flying head, use of a contact head has also been proposed so as to further shorten the distance from the medium.
The magnetic recording medium to be mounted on the magnetic disk apparatus is prepared usually by forming a NiP layer on the surface of a substrate made of e.g. an aluminum alloy, conducting a required smoothing treatment, texturing treatment or the like, and subsequently forming e.g. a metal base layer, a magnetic layer (information recording layer), a protective layer and a lubricant layer thereon. Otherwise, it may be formed by subsequently forming e.g. a metal base layer, a magnetic layer (information recording layer), a protective layer and a lubricant layer on the surface of a substrate made of e.g. glass. As the magnetic recording medium, a longitudinal magnetic recording medium and a perpendicular magnetic recording medium are mentioned. On the longitudinal magnetic recording medium, longitudinal recording is usually conducted.
The protective layer on the magnetic layer prevents damages of the magnetic layer due to impact of the flying magnetic head or sliding of the contact head, and the lubricant layer imparts lubricity between the magnetic head and the medium. By the present constitution, recording and reproducing by a flying/contact magnetic head becomes possible. Use of a flying/contact head can shorten the distance between the magnetic layer and the head, whereby information recording with a significantly high density becomes possible as compared with an optical disk or a photomagnetic disk employing a head of another type.
The density of the magnetic recording medium becomes high acceleratingly year by year, and the density becomes high by an annual rate of at least 60% in recent years. Many technique may be mentioned to realize this high density, and it is attempted, for example, to employ a GMR head as a magnetic head which is a magnetic head having its flying height decreased, to improve the magnetic material to be used for a recording layer of the magnetic disk, or to shorten the space between information recording tracks in the magnetic disk.
In each track, a magnetic pattern for control which controls the magnetic head, such as a signal to be used for position control of the magnetic head or a signal to be used for synchronous control, is formed. If the space between the information recording tracks is shortened to increase the number of tracks, signals to be used for position control of the data recording/reproducing head (hereinafter sometimes referred to as servo signals) have to be dense relative to the radius direction of the disk correspondingly, i.e. more signals have to be provided to carry out precise control.
Further, it is also strongly required to decrease the region other than the region to be used for data recording, i.e. the region used for the servo signals and the gaps between the servo region and the data recording region, in order to enlarge the data recording region and to increase the data recording capacity. Accordingly, it is necessary to increase output of the servo signals and to increase precision of the synchronous signals.
A method which has been used widely as a servo signal forming method is to make a hole in the vicinity of a head actuator of a drive (magnetic recording apparatus), insert a pin equipped with an encoder to the hole, engage said pin with the actuator, and drive the head to a precise position to record the servo signals. However, by this method, no higher precision than the limit of the recording by a magnetic head can be obtained.
Accordingly, as a magnetic printing method to a magnetic disk, a method of patterning a soft magnetic material to a master disk and contacting the master disk with a magnetic disk, which is used as a shield, and applying a magnetic field from the exterior to print the magnetic pattern, has been proposed (JP-A-50-60212 (U.S. Pat. No. 3,869,711), JP-A-10-40544 (European Patent No. 915456), xe2x80x9cReadback Properties of Novel Magnetic Contact Duplication Signals with High Recording Density FDxe2x80x9d (Sugita, R et. al, Digest of InterMag 2000, GP-06, published by IEEE)).
However, this method can be applied to a hard disk or a floppy disk having a low coercive force, but can hardly be applied to a magnetic disk having a high coercive force.
For example, the literature by Sugita et. al reports results of application of the magnetic printing method to a floppy disk and reports that excellent results of e.g. PW50 can be obtained. However, (1) the coercive force is 2,300 Oe and relatively low, and printing can be carried out with a small external magnetic field. Further, it is considered that conditions are suitable for magnetic printing, such that (2) a floppy disk has flexibility and is likely to be in contact with a master disk, (3) the magnetic pattern to be formed is broad with a width of 5 xcexcm or 10 xcexcm, and it is easy to improve PW50, and (4) a floppy disk usually has no protective layer, whereby magnetic printing can easily be carried out.
In recent years, the coercive force of a longitudinal hard disk exceeds 3 kOe. If the coercive force of a magnetic disk is large, a larger external magnetic field is required for magnetic printing, however, if the external magnetic field is made large, the magnetic field which leaks to the surrounding becomes significant, whereby the leakage magnetic field can not adequately be shielded at the pattern boundary. Accordingly, the magnetic transition region becomes unclear, and the signal quality such as PW50 may be impaired.
Further, it is very difficult to completely contact the master disk with the magnetic recording medium to which magnetic printing is applied, and the medium may have a flaw due to the contact.
On the other hand, with respect to a perpendicular hard disk which has been developed in recent years, it is difficult to shield it by the soft magnetic material, and accordingly, it is more difficult to apply the magnetic printing method.
Under these circumstances, it is an object of the present invention to provide a magnetic recording medium having improved precision and output of signals for control such as servo signals and synchronous signals, and a method for forming a magnetic pattern for control, and to provide a magnetic recording medium with which a high density recording can be carried out and a magnetic recording apparatus in a short period of time at a low cost.
According to a first aspect of the present invention, there is provided a magnetic recording medium for recording information by forming a magnetic pattern for information thereon by a magnetic head, which is a longitudinal magnetic recording medium having a coercive force of at least 3000 Oe, and which has a magnetic pattern for control of the magnetic head preliminarily formed thereon, wherein the full width at half maximum of an isolated pulse of a reproducing signal of the magnetic pattern for control is smaller than the full width at half maximum of an isolated pulse of a reproducing signal of the magnetic pattern for information.
Namely, when a medium on which a magnetic pattern is formed by a magnetic head to record information, such as a hard disk, is a longitudinal recording medium having a high coercive force of at least 3,000 Oe, small magnetic domains can be formed clearly, and a high density recording can be carried out. By forming a magnetic pattern for control with a narrow magnetic transition region on a medium to narrow the full width at half maximum of an isolated pulse of the reproducing signal of the magnetic pattern for control (the width at the half of the maximum value of the amplitude of an isolated pulse, hereinafter sometimes referred to as PW50 (Pulse Width 50%)) so that it is smaller than the full width at half maximum of an isolated pulse of the reproducing signal for the magnetic pattern for information, the synchronous precision and the position precision of the magnetic head can be increased, whereby the high density recording medium having a high reliability can be provided. When this is applied to a medium having a higher coercive force of at least 3,300 Oe, the reliability is high, recording can be carried out with a higher density, and the effect is great.
According to a second aspect of the present invention, there is provided a magnetic recording medium for recording information by forming a magnetic pattern for information thereon by a magnetic head, which is a perpendicular magnetic recording medium, and which has a magnetic pattern for control of the magnetic head preliminarily formed thereon, wherein the full width at half maximum of an isolated pulse of a reproducing signal of the magnetic pattern for control is smaller than the full width at half maximum of an isolated pulse of a reproducing signal of the magnetic pattern for information.
In the second aspect of the present invention, by making the full width at half maximum of an isolated pulse of the reproducing signal of the magnetic pattern for control to be at most 95% of the full width at half maximum of an isolated pulse of the reproducing signal of the magnetic pattern for information, the synchronous precision and the position precision of the magnetic head can further be increased, and a high density recording medium having a higher reliability can be provided. It is more preferably at most 90%.
Here, the magnetic pattern in the present invention indicates such a state that magnetic domains are arranged to generate a signal. The magnetic pattern for control is a magnetic pattern which generates control signals such as servo signals for position control of the magnetic head or synchronous signals for synchronous control. The full width at half maximum of an isolated pulse of the reproducing signal is a pulse width (width of time or length) at an output of 50% of the maximum output (0-to-peak value) of a certain isolated pulse in the reproducing signal waveform and is also referred to as PW50.
According to a third aspect of the present invention, there is provided a magnetic recording medium for recording information by forming a magnetic pattern for information thereon by a magnetic head, which has a magnetic pattern for control of the magnetic head preliminarily formed thereon, wherein the magnetic pattern for control comprises at least two types of linear patterns which form angles of (90xc2x1xcex81) degree and (90xc2x1xcex82) degree wherein xcex81 greater than xcex82, 0xc2x0 less than xcex81xe2x89xa645xc2x0 and 0xc2x0xe2x89xa6xcex82 less than 45xc2x0, respectively, with the relative movement direction of the magnetic head, and which satisfy the formula:
P(90xc2x1xcex81)/P(90xc2x1xcex82)xe2x89xa70.9xc3x97cos(xcex81xe2x88x92xcex82)
where P(90xc2x1xcex81) and P(90xc2x1xcex82) are outputs of the isolated pulses of reproducing signals of said linear patterns.
Namely, with respect to a medium on which a magnetic pattern is formed by a magnetic head to record information such as a hard disk, by using, as a magnetic pattern for control, an inclined linear pattern represented by a magnetic pattern for position control by phase control, position control of the magnetic head can be carried out with a high precision. By increasing the output of such an inclined linear pattern to satisfy the above formula, the position precision of the magnetic head can be increased.
Accordingly, the present invention is extremely effective when applied to a case of including a magnetic pattern for position control by phase control.
Further, to secure stable magnetization at room temperature, the temperature at which the magnetization of a magnetic layer is erased is preferably high. Further, the magnetic domains of a magnetic pattern can clearly be formed when the difference between the room temperature and the magnetization erasure temperature is large. Accordingly, the magnetization erasure temperature is preferably at least 100xc2x0 C. The magnetization erasure temperature may, for example, be in the vicinity of the Curie temperature (slightly lower than the Curie temperature) or in the vicinity of the compensatory temperature.
Further, to prevent damage of the medium due to impact with the magnetic head or sliding of the contact head during recording and reproducing, it is preferred to provide a protective layer on the magnetic layer. The thickness is preferably at most 50 nm to shorten the distance between the magnetic layer and the head during recording and reproducing. In a case where the recording medium has a plurality of magnetic layers, a protective layer may be provided on the magnetic layer which is closest to the surface. When the protective layer is made of diamond-like carbon, the magnetic layer will hardly be damaged by the head.
Further, it is preferred to provide a lubricant layer on the protective layer to impart lubricity between the medium and the head. The lubricant layer is preferably thin so as not to inhibit formation of the magnetic pattern, and is preferably at most 10 nm.
Further, in order not to inhibit the running stability of the flying/contact head, the surface roughness Ra of the medium is preferably at most 3 nm. Here, the medium surface roughness Ra is roughness of the surface of the medium not including the lubricant layer, and is a value obtained by measuring the roughness by means of a feeler type surface roughness meter at a measurement length of 400 xcexcm, and calculating the measured value in accordance with JIS B0601. It is more preferably at most 1.5 nm.
According to a fourth aspect of the present invention, there is provided a method for producing the above magnetic recording medium, which comprises a step of locally heating the magnetic layer on the medium, and a step of applying an external magnetic field to the magnetic layer of the medium to form a magnetic pattern for control.
According to the fourth aspect of the present invention, a magnetic pattern for control with a high quality of reproducing signals can efficiently be formed with a high precision, on a longitudinal hard disk on which recording and reproducing is carried out by a magnetic head and which has a high coercive force of at least 3,000 Oe. Namely, a pattern which has a small magnetic transition width, which has an extremely steep magnetic transition at the boundary of magnetic domains, which has a small full width at half maximum of an isolated pulse of the reproducing signal, and which has a high quality, can be formed.
Particularly, by applying an external magnetic field to preliminarily magnetize the magnetic layer homogeneously in a desired direction, and simultaneously with locally heating the magnetic layer of the medium, applying an external magnetic field to magnetize the heated area in the direction opposite to said desired direction to form a magnetic pattern for control, a desired saturation recording can be carried out, whereby a magnetic pattern having a large output of the reproducing signals can be obtained.
Further, according to the mode of applying an external magnetic field simultaneously with the local heating to magnetize the heated area, the coercive force of a magnetic recording medium having a high coercive force, which can hardly be magnetized by a conventional magnetic printing method, can adequately be lowered by heating to magnetize the medium, whereby such a medium can easily be magnetized with a weak magnetic field.
Here, the desired magnetization direction is the same or opposite direction to the running direction of the data writing/reproducing head (relative movement direction of the medium and the head) in a case where the easy axis is in a plane direction, or is a direction perpendicular thereto in a case where the easy axis is perpendicular to the plane direction.
Further, to preliminarily magnetize the magnetic layer homogeneously in a desired direction by applying an external magnetic field, is usually to homogeneously magnetize the entire magnetic layer, however, a part of the magnetic thin layer may be magnetized so long as the region on which the magnetic pattern is formed is homogeneously magnetized.
The present method is effective when applied to formation of a servo pattern to be used for position control of the data recording/reproducing magnetic head, which is simple and to which a severe precision is required, or formation of a standard pattern for recording said servo pattern. Since a high precision servo pattern or standard pattern can be obtained, the present method is effective when applied to a high density medium such as one having a track density of at least 40 kTPI.
Further, according to the present method, a magnetic pattern including a pattern which is present in an inclined direction to the running direction of the magnetic head, which has conventionally been difficult to form, can easily be formed. Further, the magnetic pattern having a high signal intensity can be obtained. The present method is particularly suitable for an inclined pattern of e.g. phase servo signals.
To form a more precise magnetic pattern, as the means of heating, it is preferred to employ energy beam in view of easiness of power control and control of the size of the area to be heated. It is preferred to employ pulse-like energy beam to control the area to be heated and to control the heating temperature. The energy beam may be one capable of partially heating the surface of the recording layer, and preferred is laser since irradiation of energy beam on an unnecessary area can be prevented.
The continuous laser beam may be formed into pulses by an optical component, but particularly preferred is use of a pulse laser light source. The pulse laser light source intermittently oscillates laser beam pulse-wise, and with which irradiation of laser beam having a high peak power can be carried out in an extremely short period of time, whereby heat is hardly be accumulated.
Further, when the magnetic layer is irradiated with energy beam by means of a mask to form a magnetic pattern on the magnetic recording medium, not only the precision of the magnetic pattern tends to be high, but also a pattern having a free shape can easily be formed in a short period of time. The mask may be one which forms gradation of energy beam on the surface of the medium corresponding to the magnetic pattern to be formed when irradiated with energy beam.
According to a fifth aspect of the present invention, there is provided a magnetic recording apparatus which comprises a magnetic recording medium, a driving component which drives the magnetic recording medium in a recording direction, a magnetic head comprising a recording component and a reproducing component, a means of moving the magnetic head relatively to the magnetic recording medium, and a recording/reproducing signal processing means which inputs a recording signal to the magnetic head and outputs a reproducing signal from the magnetic head, wherein the magnetic recording medium is any magnetic recording medium as described above. With such a magnetic recording apparatus, a high density recording can be carried out at a low cost.
As the magnetic head, usually a flying/contact magnetic head is used so as to carry out a high density recording.
Further, it is possible to easily obtain a precise servo signal by a magnetic recording apparatus wherein a magnetic recording medium is incorporated in the apparatus, then the magnetic pattern for control is reproduced by the magnetic head to obtain a signal, and a servo burst signal is recorded by the magnetic head employing the above signal as a standard. In such a case, if a signal recorded as a magnetic pattern by the present invention remains on a region which is not used as the user data region, after the servo burst signal is recorded by the magnetic head, even if the position of the magnetic head is shifted from the original position due to a certain disturbance, the magnetic head can easily be returned to the desired position, and accordingly a magnetic recording apparatus wherein signals by both writing methods are present has a high reliability.
Now, the present invention will be described in further detail with reference to the preferred embodiments.